1. Field of the Invention
This invention relates generally to a photographic camera exposure control circuit for controlling the maximum exposure time out period and, more particularly, to a photographic camera exposure control circuit for providing either a shortened or extended maximum exposure interval time out period dependent upon camera-to-subject distance as determined directly by means of sonic ranging.
2. Description of the Prior Art
In the photographic art, exposure control systems embodying scanning shutter blade elements which operate to vary the exposure aperture areas with time during the exposure interval are well known as indicated by U.S. Pat. No. 3,942,183, entitled "Camera with Pivoting Blades", by G. Whiteside, issued Mar. 2, 1976, in common assignment herewith. Such scanning shutter blade mechanisms generally include a pair of counter-reciprocating shutter blade elements each having a primary aperture that traverses the optical axis of the camera during the exposure interval. The primary apertures are shaped so that upon overlying one another during countermovement of the blades, there is defined an effective exposure aperture value which increases to a maximum value in a determinate period of time.
Exposure control is provided by a pair of secondary photocell apertures in the respective shutter blade elements which admit scene light to a photoresponsive element in correspondence with the scene light admitted to the focal plane during shutter blade movement through an exposure cycle. The output from the photoresponsive element is directed to an integration circuit which triggers upon reaching an integration level corresponding to a desired exposure value to terminate the exposure interval by returning the shutter blade elements back to their initial scene light blocking position.
Such exposure control systems may be utilized with a source of artificial illumination such as a flash bulb or electronic flash to provide artificial illumination not only during conditions of low ambient scene light intensity but also under conditions of high ambient scene light intensity where it becomes desirable to provide the artificial illumination to fill in the photographic subject against a brightly back lit scene as is more fully disclosed in U.S. Pat. No. 4,023,187, entitled "Exposure Control System with Fill Flash Race Condition", by E. Shenk, issued May 10, 1977, in common assignment herewith. The aforementioned artificial illumination control system operates under conditions of low ambient scene light intensity to fire the source of artificial illumination at a predetermined time period subsequent to the initiation of the exposure interval. Under conditions where the photographic subject is within the effective range of the flash and provides average scene light reflection, the light integration circuit will integrate the reflected scene light until reaching an integration level corresponding to a desired exposure value to terminate the exposure interval by returning the shutter blade elements back to their initial scene light blocking position.
However, under conditions where the photographic subject provides for a low degree artificial scene light reflection or is located beyond the effective range of the flash, there may be insufficient reflected scene light for the integration circuit to reach the integration level corresponding to the desired exposure value. Thus, it is also well known to provide an exposure interval time out circuit for limiting the maximum time that the shutter blade elements may remain in the scene light unblocking position. Such time out circuits are included in both SX-70 and Pronto! type cameras manufactured and sold by Polaroid Corporation and provide either an extended maximum exposure interval time out period in the order of 1-20 seconds when the source of artificial illumination is disconnected from the camera or a shortened maximum exposure interval time out period in the order of 65 milliseconds when the source of artificial illumination is connected to the camera. Such a shortened maximum exposure interval time out period can provide generally satisfactory results in situations where the photographic subject is located within the effective range of the flash and has a low scene light reflectance characteristic or where the subject is located just beyond the effective range of the flash and where there is still substantial reflected scene light albeit insufficient to cause the integration circuit to reach the required integration level corresponding to the desired exposure value within the shortened maximum exposure interval time out period. Under the aforementioned conditions, the photographic film may be slightly underexposed but may nevertheless provide a generally satisfactory photograph which is not blurred.
The above-mentioned extended maximum exposure time out interval is suitable for use under conditions where the photographic subject may be so far removed from the effective range of the flash that there is little or no reflected flash light. Under these conditions, it is desirable to extend the maximum time out period for the exposure interval far beyond the maximum allowable time to which an exposure interval may be extended without incurring the adverse blurring effects from the normally expected hand motion of a handheld camera. Under these conditions, it is preferable to utilize a tripod or some other stable means for mounting the camera so as not to incur adverse blurring effects. Thus, with such an extended maximum exposure interval time out period, it is possible for the photographic film to record all available ambient scene light such as starlight, street lights or building lights. Heretofore, whether the camera provided the photographer with an extended or shortened maximum exposure interval time out period depended upon whether the photographer connected the source of artificial illumination to the camera or not as previously discussed with respect to Polaroid's SX-70 and Pronto! type cameras. Thus, the photographer had to evaluate the camera-to-subject range as well as the probable flash light reflectivity of the subject in order to decide whether the best results could be achieved by either using the artificial illumination with a shortened maximum exposure interval time out period or by not using the artificial illumination and relying solely on the extended maximum exposure interval time out period to record all available scene light.
Therefore, it is a primary object of this invention to provide a photographic camera exposure control circuit for selectively differentiating between conditions where the photographic subject is located close enough to the camera that there is likely to be substantial but insufficient reflected flash light to effect the termination of exposure solely as a function of scene light integration and it is desirable to provide a shortened maximum exposure interval time out period and conditions where the photographic subject is located far enough from the camera that there is likely to be little or no reflected flash light and it is desirable to provide an extended maximum exposure interval time out period.
It is a further object of this invention to provide a photographic camera exposure control circuit for determining the camera-to-subject distance directly by sonic ranging and for automatically responding to the sonically determined subject distance to provide either a shortened maximum exposure interval time out period where the subject is located close enough to the camera that it is likely to be substantial but insufficient reflected flash light to effect the termination of exposure solely as a function of scene light integration or an extended maximum exposure interval time out period under conditions where the subject is located far enough from the camera that there is likely to be virtually no reflected flash light.
Other objects of the invention will be in part obvious and will in part appear hereinafter. The invention accordingly comprises a mechanism and system possessing a construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.